On 2024/1/26 16:57, Baokun Li wrote: > We can trigger a slab-out-of-bounds with the following commands: > > mkfs.ext4 -F /dev/$disk 10G > mount /dev/$disk /tmp/test > echo 2147483647 > /sys/fs/ext4/$disk/mb_group_prealloc > echo test > /tmp/test/file && sync > > ================================================================== > BUG: KASAN: slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists+0x8a/0x200 [ext4] > Read of size 8 at addr ffff888121b9d0f0 by task kworker/u2:0/11 > CPU: 0 PID: 11 Comm: kworker/u2:0 Tainted: GL 6.7.0-next-20240118 #521 > Call Trace: > dump_stack_lvl+0x2c/0x50 > kasan_report+0xb6/0xf0 > ext4_mb_find_good_group_avg_frag_lists+0x8a/0x200 [ext4] > ext4_mb_regular_allocator+0x19e9/0x2370 [ext4] > ext4_mb_new_blocks+0x88a/0x1370 [ext4] > ext4_ext_map_blocks+0x14f7/0x2390 [ext4] > ext4_map_blocks+0x569/0xea0 [ext4] > ext4_do_writepages+0x10f6/0x1bc0 [ext4] > [...] > ================================================================== > > The flow of issue triggering is as follows: > > // Set s_mb_group_prealloc to 2147483647 via sysfs > ext4_mb_new_blocks > ext4_mb_normalize_request > ext4_mb_normalize_group_request > ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc > ext4_mb_regular_allocator > ext4_mb_choose_next_group > ext4_mb_choose_next_group_best_avail > mb_avg_fragment_size_order > order = fls(len) - 2 = 29 > ext4_mb_find_good_group_avg_frag_lists > frag_list = &sbi->s_mb_avg_fragment_size[order] > if (list_empty(frag_list)) // Trigger SOOB! > > At 4k block size, the length of the s_mb_avg_fragment_size list is 14, but > an oversized s_mb_group_prealloc is set, causing slab-out-of-bounds to be > triggered by an attempt to access an element at index 29. > > Therefore it is not allowed to set s_mb_group_prealloc to a value greater > than s_clusters_per_group via sysfs, and to avoid returning an order from > mb_avg_fragment_size_order() that is greater than MB_NUM_ORDERS(sb). > > Fixes: 7e170922f06b ("ext4: Add allocation criteria 1.5 (CR1_5)") > CC: stable@xxxxxxxxxxxxxxx > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> Looks good to me. Reviewed-by: Zhang Yi <yi.zhang@xxxxxxxxxx> > --- > fs/ext4/mballoc.c | 2 ++ > fs/ext4/sysfs.c | 9 ++++++++- > 2 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index f44f668e407f..1ea6491b6b00 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -832,6 +832,8 @@ static int mb_avg_fragment_size_order(struct super_block *sb, ext4_grpblk_t len) > return 0; > if (order == MB_NUM_ORDERS(sb)) > order--; > + if (WARN_ON_ONCE(order > MB_NUM_ORDERS(sb))) > + order = MB_NUM_ORDERS(sb) - 1; > return order; > } > > diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c > index 6f9f96e00f2f..60ca7b2797b2 100644 > --- a/fs/ext4/sysfs.c > +++ b/fs/ext4/sysfs.c > @@ -29,6 +29,7 @@ typedef enum { > attr_trigger_test_error, > attr_first_error_time, > attr_last_error_time, > + attr_group_prealloc, > attr_feature, > attr_pointer_pi, > attr_pointer_ui, > @@ -211,13 +212,14 @@ EXT4_ATTR_FUNC(sra_exceeded_retry_limit, 0444); > > EXT4_ATTR_OFFSET(inode_readahead_blks, 0644, inode_readahead, > ext4_sb_info, s_inode_readahead_blks); > +EXT4_ATTR_OFFSET(mb_group_prealloc, 0644, group_prealloc, > + ext4_sb_info, s_mb_group_prealloc); > EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal); > EXT4_RW_ATTR_SBI_UI(mb_stats, s_mb_stats); > EXT4_RW_ATTR_SBI_UI(mb_max_to_scan, s_mb_max_to_scan); > EXT4_RW_ATTR_SBI_UI(mb_min_to_scan, s_mb_min_to_scan); > EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs); > EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request); > -EXT4_RW_ATTR_SBI_PI(mb_group_prealloc, s_mb_group_prealloc); > EXT4_RW_ATTR_SBI_UI(mb_max_linear_groups, s_mb_max_linear_groups); > EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb); > EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error); > @@ -380,6 +382,7 @@ static ssize_t ext4_generic_attr_show(struct ext4_attr *a, > > switch (a->attr_id) { > case attr_inode_readahead: > + case attr_group_prealloc: > case attr_pointer_pi: > case attr_pointer_ui: > if (a->attr_ptr == ptr_ext4_super_block_offset) > @@ -453,6 +456,10 @@ static ssize_t ext4_generic_attr_store(struct ext4_attr *a, > return ret; > > switch (a->attr_id) { > + case attr_group_prealloc: > + if (t > sbi->s_clusters_per_group) > + return -EINVAL; > + fallthrough; > case attr_pointer_pi: > if ((int)t < 0) > return -EINVAL; >